In a large pot, boil salted water and cook the fettuccine according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet over medium-high heat, add the olive oil. Once hot, add the sliced flank steak, season with salt and pepper, and sear for about 3-4 minutes until browned. Remove the steak from the skillet and set aside.
In the same skillet, add the minced garlic and sauté for about 30 seconds until fragrant. Pour in the beef broth and heavy cream, stirring well to combine. Bring the mixture to a simmer.
Stir in the cherry tomatoes and spinach. Allow them to cook for about 2-3 minutes, until the spinach wilts and the tomatoes soften.
Return the seared steak to the skillet, along with the cooked fettuccine. Toss everything together, adding reserved pasta water a little at a time until the sauce reaches your desired consistency.
Stir in the grated Parmesan cheese and mix until incorporated. Adjust seasoning with salt and pepper if needed.
Plate the creamy steak pasta immediately, garnished with fresh basil for a pop of color and flavor.